In recent years, a technique referred to as OpenFlow has been proposed (see Patent Literature (PTL) 1 and Non-Patent Literatures (NPLs) 1 and 2). OpenFlow recognizes communications as end-to-end flows and performs path control, failure recovery, load balancing, and optimization on a per-flow basis. Each OpenFlow switch according to Non-Patent Literature 2 has a secure channel for communication with an OpenFlow controller and operates according to a flow table suitably added or rewritten by the OpenFlow controller. In the flow table, a set of the following three is defined for each flow: matching rules (Header Fields) against which a packet header is matched; flow statistical information (Counters); and Instructions that define a processing content(s) (see FIG. 10).
For example, when an OpenFlow switch receives a packet, the OpenFlow switch searches the flow table for an entry having a matching rule (see Header Fields in FIG. 10) that matches header information of the received packet. If, as a result of the search, the OpenFlow switch finds an entry matching the received packet, the OpenFlow switch updates the flow statistical information (Counters) and processes the received packet on the basis of a processing content(s) (packet transmission from a specified port, flooding, dropping, etc.) written in the Instructions field of the entry. If, as a result of the search, the OpenFlow switch does not find an entry matching the received packet, the OpenFlow switch transmits an entry setting request to the OpenFlow controller via the secure channel. Namely, the OpenFlow switch requests the OpenFlow controller to determine a processing content for the received packet. The OpenFlow switch receives a flow entry defining a processing content(s) and updates the flow table. In this way, by using an entry stored in the flow table as a processing rule (packet processing instruction), the OpenFlow switch performs packet forwarding.
To realize broadcast or multicast in networks disclosed in the above Patent Literature 1 and Non-Patent Literatures 1 and 2, flow entries for forwarding packets via a plurality of ports are set in each of the relevant OpenFlow switches.
In addition, Patent Literature 2 discloses a LAN relay apparatus that performs, when an uplink or a stack link reaches a congestion state, flow control without stopping input and output via input and output ports and without affecting communication that is irrelevant to the congestion state.
PTL 1:
    International Publication No. 2008/095010PTL 2:    Japanese Patent Kokai Publication No. 2000-270002ANPL 1:    Nick McKeown, and seven others, “OpenFlow: Enabling Innovation in Campus Networks,” [online], [searched May 8, 2012], Internet <URL:http://www.openflow.org/documents/openflow-wp-latest.pd>NPL 2:    “OpenFlow Switch Specification” Version 1.1.0 Implemented (Wire Protocol 0x02), [online], [searched on May 8, 2012], Internet <URL:http://www.openflow.org/documents/openflow-spec-v1.1.0.pdf>